1. Field
Embodiments relate to a motor control apparatus and a motor control method thereof in which a velocity of a motor is controlled according to a velocity profile to drive the motor.
2. Description of the Related Art
In general, a robot controller to control movement of a robot performs control of a position, a velocity, and an acceleration of a motor provided on a robot joint per control cycle according to data, such as a target position, a target velocity, a target acceleration time, and a target deceleration time input by a user.
Here, the motor of the robot joint is driven according to a velocity profile.
In the velocity profile to drive the motor, a velocity zone is divided into an acceleration section, a constant velocity section, and a deceleration section. The velocity profile is defined as a polynomial expression from the position, the velocity, the acceleration time, and the deceleration time of the motor influencing the drive of the motor.
The motor is driven following the above-defined velocity profile. Further, while the motor is driven, the velocity profile is not changed.
The velocity profile is generated based on parameters, such as the position, the velocity, the acceleration time, and the deceleration time, input by the user.
In case of the velocity of the motor, an allowance torque of the motor tends to decrease as the motor reaches a high velocity region of a velocity-torque curve, generally called an NT-curve. Therefore, in order to stably use the motor in all velocity regions, a load of the motor is adjusted so as to generate only a small torque if the motor is driven within a rated RPM or at a high velocity.
However, motion-related parameters of the robot, such as velocity, acceleration, etc., need to be set such that reliability allowing the robot to stably move within all motion regions in which the robot is movable is assured and particularly, the same reliability is assured under unfavorable conditions, such as a section requiring a high torque due to uniqueness or high inertia.
Among several methods to set the parameters of the robot, the most general method is a method in which the highest velocity is set to a rated RPM of the motor, a velocity profile is generated based on the velocity, and other regions higher than the velocity are excluded.
If the motor is used under the above condition, the motor generates the maximum torque in all velocity regions, and the motor is easy to design and control. Further, since there is a margin from the rated RPM to the maximum RPM region, a region where the velocity is unexpectedly rapidly raised due to uniqueness is included, and thus considerably high reliability is assured.
However, in a normal case, a region higher than the rated RPM is not used, and thus efficiency of the velocity of the motor is considerably low.